A ''city within a city,'' it boasted a 1,000-ton ice plant; Gargantuan coal-fired steam engines capable of powering 12,000 electric lights; a movable stage fronting the ornate, 2,000-seat grand ballroom; and one of the grandest grand staircases in all hoteldom.

In no time the Bellevue Stratford became the city's premier hotel. It was a standard setting for important political events and Main Line wedding receptions. Out-of-towners flocked there like birds heading south for the winter.

But in the 1950s modernization efforts destroyed many of the architectural features Boldt had spared no expense to create. Hard times in the hotel industry during the 1960s further eroded the Bellevue's luster. And the Legionnaire's disease scare in 1976 ended in the closing of the hotel, some thought for good.

Now, thanks to two prestigious hotel corporations and seven community-minded financial institutions here, the Bellevue Stratford is not only open for business but is once again widely considered ''the showplace of Philadelphia.''

After a $25 million renovation, the hotel reopened in 1979 as the Fairmont Hotel, managed by the Fairmont hotel group. Two years later the Westin Hotels assumed management, together with an equity interest, and changed the hotel's name back to its original. Westin itself plans substantial renovations, as well as two major additions and a super-deluxe sports-recreation complex complete with swimming pool and running track and a badly needed 500-car garage.

''What I'm trying to do is to reestablish the hotel as the premier hotel in Philadelphia,'' says F. Bart Moore, the general manager.

''We will maintain and are maintaining a high quality of service in the hotel.''

One frequent gauge of the quality of service of any hotel is its ratio of employees to rooms. The Bellevue Stratford rates high indeed, with 600 employees for 569 rooms. The hotel's occupancy rate is climbing higher every month.